What is Overheating?
Overheating occurs when the indoor temperature of a building (an intermediate climate space) exceeds occupant comfort levels. This occurs typically because of excessive heat gains from solar radiation and internal heat sources that are trapped due to high insulation and airtight construction. This scenario has resulted in thermal discomfort and health hazards, especially in NZEBs (Mulville et al., 2025; Rijal & Nakaya, 2012).
Overheating vs Thermal
Thermal comfort of indoor settings is critical for occupant health in NZEBs. However, with good control of essential environmental parameters (temperature, air movement, humidity), comfortable, health-friendly indoor climates conducive to work are achievable. The main conditions for thermal comfort are:
1. Indoor Temperature Control: By maintaining a stable temperature within an optimal range (20-24°C), this control must adapt to seasonal and external climate changes (HSE, 2024).
2. Balanced Environmental Factors: By ensuring a balanced interaction between air temperature, air velocity, and radiant temperature, this can be qualified by models such as PMV and PPD, as they help to achieve thermal sensation (Mulville et al., 2025), (Balbis-Morejón et al., 2020), (Rizqi Amelia Aristawati, 2019), (Rijal & Nakaya, 2012).
3. Effective Ventilation and Humidity Regulation: Pollutant build-up could be prevented, and overall comfort can be obtained by providing a continuous supply of fresh and filtered air (BEAM, 2024).
Designing for Thermal Comfort
Designing for comfort in NZEBs requires balancing energy efficiency with maintaining indoor conditions within acceptable comfort zones.
Architects use guidelines such as ASHRAE Standard 55 and CIBSE TM59, along with national regulations such as the Irish Part L, to a performance target for the optimal temperature, humidity, and airflow. Simulation tools often incorporate PMV versus PPD analyses to identify designs that contribute towards the mitigation of overheating, while ensuring occupants' wellbeing, even under climate change (Mulville et al., 2025).
“Overheating and poor air quality can transform a home into a suffocating trap, whereby each breath feels heavy, and every space becomes a source of stress and discomfort, leaving occupants both physically and emotionally drained”.
Average temperature increases in degrees Celsius predicted for Ireland by 2050, 2070 and 2100 (Nolan & Flanagan, 2020)
Comfort Today can be Discomfort Tomorrow.
While NZEBs are designed to deliver maximum thermal comfort at existing conditions, the increase in outdoor temperatures will lead to these same buildings experiencing overheating.
The high-performance insulation and airtight construction that minimize energy loss can also hold excess heat in, as outside temperatures rise, and make today’s comfort tomorrow’s discomfort.